Titanium can be considered a relatively difficult material to mill as the properties thereof can quickly degrade an end mill. Such degradation is believed, in theory, to be at least in part due to heat transfer of a workpiece made of titanium to an end mill machining the workpiece.
Aside from heat transfer, another consideration when designing end mills is evacuation of chips. Flute shape is accordingly taken into account during end mill design. CN 20145538, CN 102303158 and CN 202199817 disclose end mills having flutes shape in accordance with different mathematical models.
Yet another consideration is reduction of end mill chatter. Reduction of chatter can be achieved, in theory, by designing end mills with asymmetric features, for example, as disclosed in U.S. Pat. Nos. 6,991,409, 7,306,408 and 8,007,209. FIG. 1 of U.S. Pat. No. 8,007,209 also disclosing an end mill having serrations (FIG. 1, reference numeral 7).
While many end mills appear similar, upon close inspection there are often many small but relevant differences, some differences being critical as to whether an end mill can achieve a desired machining operation of a particular type of material or under particular cutting conditions.
Commonly, cutting edges are placed at different index angles with respect to each other, helix, radial rake and axial rake angles may vary at different cutting edges and even may vary along a single cutting edge. Orientation, position and size of each element in an end mill may have significant effect on the performance thereof.
In view of the extremely large number of variations of design possible, there is ongoing research to try and find more efficient end mills, especially for machining specific materials such as titanium.